Using the TI-83 normal approximation you would get .2248 from normalcdf(-999,10,12.5,sd) with the continuity correction you would get .2727 from normalcdf(-999,10.5,12.5,sd). For those of you unfamiliar with TI-83 normalcdf(lowerbound, upperbound, mean, sd) returns area under curve quickly.
The student had done simply binompdf(100,0.125) stored to L1 and then did sum(L1,1,11) and arrived with .280999. TI-83 binompdf(100,0.125) returns all probabilities from 0 to 100 for p = 1/8. He summed items 1 to 11 to get P(0) through P(10). He was, with ease at which he had done this, amazed that anyone would do it the other way.
----- End of forwarded message from John Magee -----
I can't say anything about the TI-83, but all of these computational shortcuts and approximations are relative to some particular computing technology. For example, the "computational formula" for variance and standard deviation harks back to mechanical desktop calculators. The methods seem to take on a life of their own and continue to be used long after there is any need for them. One of the functions of youth is to question this!-)
_ | | Robert W. Hayden | | Department of Mathematics / | Plymouth State College MSC#29 | | Plymouth, New Hampshire 03264 USA | * | Rural Route 1, Box 10 / | Ashland, NH 03217-9702 | ) (603) 968-9914 (home) L_____/ firstname.lastname@example.org fax (603) 535-2943 (work)